Fast acquisition of traffic channels for a highly variable data rate reverse link of a CDMA wireless communication system

ABSTRACT

A method for monitoring idling mode connections between a base station and idling subscriber units that are powered on, but not actively sending data, is provided. The method includes making available a plurality of orthogonal subchannels within at least one Code Division Multiple Access (CDMA) radio frequency (RF) channel. A shared orthogonal subchannel is assigned to at least two different idling subscriber units, but utilizing different time slots of the shared orthogonal subchannels. For each idling subscriber unit assigned the shared orthogonal subchannel, a respective heartbeat signal is sent within its assigned time slot at a data rate that is low enough to maintain bit synchronization with the base station. The respective heartbeat signals are tracked within the assigned time slots by selecting an assigned time slot within the shared orthogonal subchannel, retrieving a previous tracking of a respective heartbeat signal for an idling subscriber unit associated with the assigned time slot, determining a current tracking of the respective heartbeat signal for the idling subscriber unit associated with the assigned time slot, and updating the tracking of the idling subscriber unit associated with the assigned time slot based upon its current and previous trackings.

RELATED APPLICATIONS

This application is a continuation of application Ser. No. 09/730,376,filed Dec. 5, 2000, now U.S. Pat. No. 6,707,804, which is a continuationof application Ser. No. 09/088,413, filed Jun. 1, 1998, now U.S. Pat.No. 6,222,832. The entire teachings of the above applications areincorporated herein by reference.

BACKGROUND OF THE INVENTION

The increasing use of wireless telephones and personal computers has ledto a corresponding demand for advanced telecommunication services thatwere once thought to only be meant for use in specialized applications.In the 1980's, wireless voice communication became widely availablethrough the cellular telephone network. Such services were at firsttypically considered to be the exclusive province of the businessmanbecause of expected high subscriber costs. The same was also true foraccess to remotely distributed computer networks, whereby until veryrecently, only business people and large institutions could afford thenecessary computers and wireline access equipment. As a result of thewidespread availability of both technologies, the general population nowincreasingly wishes to not only have access to networks such as theInternet and private intranets, but also to access such networks in awireless fashion as well. This is particularly of concern for the usersof portable computers, laptop computers, hand-held personal digitalassistants and the like who would prefer to access such networks withoutbeing tethered to a telephone line.

There still is no widely available satisfactory solution for providinglow cost, broad geographical coverage, high speed access to theInternet, private intranets, and other networks using the existingwireless infrastructure. This situation is most likely an artifact ofseveral unfortunate circumstances. For one, the typical manner ofproviding high speed data service in the business environment over thewireline network is not readily adaptable to the voice grade serviceavailable in most homes or offices. Such standard high speed dataservices also do not lend themselves well to efficient transmission overstandard cellular wireless handsets. Furthermore, the existing cellularnetwork was originally designed only to deliver voice services. As aresult, the emphasis in present day digital wireless communicationschemes lies with voice, although certain schemes such as CDMA doprovide some measure of asymmetrical behavior for the accommodation ofdata transmission. For example, the data rate on an IS-95 forwardtraffic channel can be adjusted in increments from 1.2 kbps up to 9.6kbps for so-called Rate Set 1 and in increments from 1.8 kbps up to 14.4kbps for Rate Set 2.

Existing systems therefore typically provide a radio channel which canaccommodate maximum data rates only in the range of 14.4 kilobits persecond (kbps) at best in the forward direction. Such a low data ratechannel does not lend itself directly to transmitting data at rates of28.8 or even 56.6 kbps that are now commonly available using inexpensivewireline modems, not to mention even higher rates such as the 128 kbpswhich are available with Integrated Services Digital Network (ISDN) typeequipment. Data rates at these levels are rapidly becoming the minimumacceptable rates for activities such as browsing web pages. Other typesof data networks using higher speed building blocks such as DigitalSubscriber Line (xDSL) service are just now coming into use in theUnited States. However, their costs have only been recently reduced tothe point where they are attractive to the residential customer.

Although such networks were known at the time that cellular systems wereoriginally deployed, for the most part, there is no provision forproviding higher speed ISDN- or xDSL-grade data services over cellularnetwork topologies. Unfortunately, in wireless environments, access tochannels by multiple subscribers is expensive and there is competitionfor them. Whether the multiple access is provided by the traditionalFrequency Division Multiple Access (FDMA) using analog modulation on agroup of radio carriers, or by newer digital modulation schemes thatpermit sharing of a radio carrier using Time Division Multiple Access(TDMA) or Code Division Multiple Access (CDMA), the nature of the radiospectrum is that it is a medium that is expected to be shared. This isquite dissimilar to the traditional environment for data transmission,in which the wireline medium is relatively inexpensive to obtain, and istherefore not typically intended to be shared.

Other considerations are the characteristics of the data itself. Forexample, consider that access to web pages in general is burst-oriented,with asymmetrical data rate transmission-requirements. In particular,the user of a remote client computer first specifies the address of aweb page to a browser program. The browser program then sends this webpage address data, which is typically 100 bytes or less in length, overthe network to a server computer. The server computer then responds withthe content of the requested web page, which may include anywhere from10 kilobytes to several megabytes of text, image, audio, or even videodata. The user then may spend at least several seconds or even severalminutes reading the content of the page before requesting that anotherpage be downloaded. Therefore, the required forward channel data rates,that is, from the base station to the subscriber, are typically manytimes greater than the required reverse channel data rates.

In an office environment, the nature of most employees' computer workhabits is typically to check a few web pages and then to do somethingelse for extended period of time, such as to access locally stored dataor to even stop using the computer altogether. Therefore, even thoughsuch users may expect to remain connected to the Internet or privateintranet continuously during an entire day, the actual overall nature ofthe need to support a required data transfer activity to and from aparticular subscriber unit is actually quite sporadic.

SUMMARY OF THE INVENTION

Problem Statement

What is needed is an efficient scheme for supporting wireless datacommunication such as from portable computers to computer networks suchas the Internet and private intranets using widely availableinfrastructure. Unfortunately, even the most modern wireless standardsin widespread use such as CDMA do not provide adequate structure forsupporting the most common activities, such as web page browsing. In theforward and reverse link direction, the maximum available channelbandwidth in an IS-95 type CDMA system is only 14.4 kbps. Due to IS-95being circuit-switched, there are only a maximum of 64 circuit-switchedusers that can be active at one time. In practicality, this limit isdifficult to attain, and 20 or 30 simultaneous users are typically used.

In addition, the existing CDMA system requires certain operations beforea channel can be used. Both access and traffic channels are modulated byso-called long code pseudonoise (PN) sequences; therefore, in order forthe receiver to work properly it must first be synchronized with thetransmitter. The setting up and tearing down of channels thereforerequires overhead to perform such synchronization. This overhead resultsin a noticeable delay to the user of the subscriber unit.

An attractive method of increasing data rate for a given user is thesharing of channels in both the forward and reverse link direction. Thisis an attractive option, especially with the ease of obtaining multipleaccess with CDMA; additional users can be supported by simply addingadditional codes for the forward link, or code phases in the reverselink for an IS-95 system. Ideally, this subchannel overhead would beminimized so that when additional subchannels need to be allocated to aconnection, they are available as rapidly as possible.

To maintain synchronization, it is therefore advantageous to provide thesubchannels in such a way that the lowest possible speed connection isprovided on a reverse link while at the same time maintaining efficientand fast ramp-up of additional code phase channels on demand. This inturn would maximize the number of available connections while minimizingthe impact on the overall system capacity.

BRIEF DESCRIPTION OF THE INVENTION

The present invention is a service option overlay for an IS-95-like CDMAwireless communication system which accomplishes the above requirements.In particular, a number of subchannels for a forward link are definedwithin a single CDMA radio channel bandwidth, such as by assigningdifferent orthogonal codes to each sub-channel. Multiple subchannels aredefined on the reverse link by assigning different code phases of agiven long pseudonoise (PN) code to each subchannel. The instantaneousbandwidth needs of each on-line subscriber unit are then met bydynamically allocating none, one, or multiple subchannels on an asneeded basis for each network layer connection.

More particularly, the present invention efficiently provides arelatively large number of virtual physical connections between thesubscriber units and the base stations on the reverse link for extendedidle periods such as when computers connected to the subscriber unitsare powered on, but not presently actively sending or receiving data.These maintenance subchannels permit the base station and the subscriberunits to remain in phase and time synchronism. This in turn allows fastacquisition of additional subchannels as needed by allocating new codephase subchannels. Preferably, the code phases of the new channels areassigned according to a predetermined code phase relationship withrespect to the code phase of the corresponding maintenance subchannel.

In an idle mode, the subscriber unit sends a synchronization or“heartbeat” message on the maintenance subchannel at a data rate whichneed only be fast enough to allow the subscriber unit to maintainsynchronization with the base station. The duration of the heartbeatsignal is determined by considering the capture or locking range of thecode phase locking circuits in the receiver at the base station.

For example, the receiver typically has a PN code correlator running atthe code chip rate. One example of such a code correlator uses a delaylock loop consisting of an early-late detector. A loop filter controlsthe bandwidth of the loop which in turn determines how long the codecorrelator must be allowed to operate before it can guarantee phaselock. This loop time constant determines the amount of “jitter” that canbe tolerated; phase lock is typically considered to be maintainable whenthis is equal to a fraction of a chip time, such as about ⅛ of a chiptime.

The heartbeat messages are preferably sent in time slots formed on thesubchannels defined by the code phases. The use of time slotting allowsa minimum number of dedicated base station receivers to maintain theidle reverse links. In particular, the reverse maintenance channel linksare provided using multiple phases of the same long code as well as byassigning a time slot on such code to each subscriber unit. This reducesthe overhead of maintaining a large number of connections at the basestation.

Because of the time slotted nature of the reverse maintenance channel,the base station receiver can also be time shared among these variousreverse links. To permit this, during each time slot allocated to aparticular subscriber unit, the base station receiver first loadsinformation concerning the last known state of its phase lock such asthe last known state of early-late correlators. It then trains theearly-late correlators for the required time to ensure that phase lockis still valid, and stores the state of the correlators at the end ofthe time slot.

When additional subchannels are required to meet bandwidth demand, theadditional code phases are assigned in a predetermined phaserelationship with respect to the locked code in order to minimizeoverhead transmissions which would otherwise be needed from the basestation traffic channel processor. As a result, many thousands of idlesubscriber units may be supported on a single CDMA reverse link radiochannel while at the same time minimizing start up delay when channelsmust be allocated.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views.

FIG. 1 is a block diagram of a wireless communication system making useof a bandwidth management scheme according to the invention.

FIG. 2 is a diagram showing how subchannels are assigned within a givenradio forward link frequency (RF) channel.

FIG. 3 is a diagram showing how subchannels are assigned within a givenreverse link RF channel.

FIG. 4 is a state diagram for a reverse link bandwidth managementfunction in the subscriber unit; and

FIG. 5 is a state diagram of the reverse link bandwidth managementfunction in the base station.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Turning attention now to the drawings more particularly, FIG. 1 is ablock diagram of a system 100 for providing high speed data and voiceservice over a wireless connection by seamlessly integrating a digitaldata protocol such as, for example, Integrated Services Digital Network(ISDN) with a digitally modulated wireless service such as Code DivisionMultiple Access (CDMA).

The system 100 consists of two different types of components, includingsubscriber units 101-1, 101-2, . . . , 101-u (collectively, thesubscriber units 101) and one or more base stations 170. The subscriberunits 101 and base stations 170 cooperate to provide the functionsnecessary in order to provide wireless data services to a portablecomputing device 110 such as a laptop computer, portable computer,personal digital assistant (PDA) or the like. The base station 170 alsocooperates with the subscriber units 101 to permit the ultimatetransmission of data to and from the subscriber unit and the PublicSwitched Telephone Network (PSTN) 180.

More particularly, data and/or voice services are also provided by thesubscriber unit 101 to the portable computer 110 as well as one or moreother devices such as telephones 112-1, 112-2 (collectively referred toherein as telephones 112). The telephones 112 themselves may in turn beconnected to other modems and computers which are not shown in FIG. 1.In the usual parlance of ISDN, the portable computer 110 and telephones112 are referred to as terminal equipment (TE). The subscriber unit 101provides the functions referred to as a network termination type 1(NT−1). The illustrated subscriber unit 101 is in particular meant tooperate with a so-called basic rate interface (BRI) type ISDN connectionthat provides two bearer or “B” channels and a single data or “D”channel with the usual designation being 2B+D.

The subscriber unit 101 itself consists of an ISDN modem 120, a devicereferred to herein as the protocol converter 130 that performs thevarious functions according to the invention including spoofing 132 andbandwidth management 134, a CDMA transceiver 140, and subscriber unitantenna 150. The various components of the subscriber unit 101 may berealized in discrete devices or as an integrated unit. For example, anexisting conventional ISDN modem 120 such as is readily available fromany number of manufacturers may be used together with existing CDMAtransceivers 140. In this case, the unique functions are providedentirely by the protocol converter 130 which may be sold as a separatedevice. Alternatively, the ISDN modem 120, protocol converter 130, andCDMA transceiver 140 may be integrated as a complete unit and sold as asingle subscriber unit device 101. Other types of interface connectionssuch as Ethernet or PCMCIA may be used to connect the computing deviceto the protocol converter 130. The device may also interface to anEthernet interface rather than an ISDN “U” interface.

The ISDN modem 120 converts data and voice signals between the terminalequipment 110 and 112 to format required by the standard ISDN “U”interface. The U interface is a reference point in ISDN systems thatdesignates a point of the connection between the network termination(NT) and the telephone company.

The protocol converter 130 performs spoofing 132 and basic bandwidthmanagement 134 functions. In general, spoofing 132 consists of insuringthat the subscriber unit 101 appears to the terminal equipment 110, 112that is connected to the public switched telephone network 180 on theother side of the base station 170 at all times. The bandwidthmanagement function 134 is responsible for allocating and deallocatingCDMA radio channels 160 as required. Bandwidth management 134 alsoincludes the dynamic management of the bandwidth allocated to a givensession by dynamically assigning sub-portions of the CDMA radio channels160 in a manner which is more fully described below.

The CDMA transceiver 140 accepts the data from the protocol converter130 and reformats this data in appropriate form for transmission througha subscriber unit antenna 150 over CDMA radio link 160-1. The CDMAtransceiver 140 may operate over only a single 1.25 MHz radio frequencychannel or, alternatively, in a preferred embodiment, may be tunableover multiple allocatable radio frequency channels.

CDMA signal transmissions are then received and processed by the basestation equipment 170. The base station equipment 170 typically consistsof multichannel antennas 171, multiple CDMA transceivers 172, and abandwidth management functionality 174. Bandwidth management 174controls the allocation of CDMA radio channels 160 and subchannels, in amanner analogous to the subscriber unit 101. The base station 170 thencouples the demodulated radio signals to the Public Switch TelephoneNetwork (PSTN) 180 in a manner which is well known in the art. Forexample, the base station 170 may communicate with the PSTN 180 over anynumber of different efficient communication protocols such as primaryrate ISDN, or other LAPD based protocols such as IS-634 or V5.2.

It should also be understood that data signals travel bidirectionallyacross the CDMA radio channels 160. In other words, data signalsreceived from the PSTN 180 are coupled to the portable computer 110 in aforward link direction, and data signals originating at the portablecomputer 110 are coupled to the PSTN 180 in a so-called reverse linkdirection. The present invention involves in particular the manner ofimplementing the reverse link channels.

Continuing to refer to FIG. 1 briefly, spoofing 134 therefore involveshaving the CDMA transceiver 140 loop back these synchronous data bitsover the ISDN communication path to spoof the terminal equipment 110,112 into believing that a sufficiently wide wireless communication link160 is continuously available. However, only when there is actually datapresent from the terminal equipment to the wireless transceiver 140 iswireless bandwidth allocated. Therefore, the network layer need notallocate the assigned wireless bandwidth for the entirety of thecommunications session. That is, when data is not being presented uponthe terminal equipment to the network equipment, the bandwidthmanagement function 134 deallocates initially assigned radio channelbandwidth 160 and makes it available for another transceiver and anothersubscriber unit 101.

In order to better understand how bandwidth management 134 and 174accomplish the dynamic allocation of radio channels, turn attention nowto FIG. 2. This figure illustrates one possible frequency plan for thewireless links 160 according to the invention. In particular, a typicaltransceiver 170 can be tuned on command to any 1.25 MHz channel within amuch larger bandwidth, such as up to 30 MHz. In the case of location inexisting cellular radio frequency bands, these bandwidths are typicallymade available in the range of from 800 to 900 MHz. For personalcommunication systems CPCS) type wireless systems, the bandwidth istypically allocated in the range from about 1.8 to 2.0 GigaHertz (GHz).In addition, there are typically two matching bands activesimultaneously, separated by a guard band, such as 80 MHz; the twomatching bands form forward and reverse full duplex link.

Each of the CDMA transceivers, such as transceiver 140 in the subscriberunit 101, and transceivers 172 in the base station 170, are capable ofbeing tuned at any given point in time to a given 1.25 MHz radiofrequency channel. It is generally understood that such 1.25 MHz radiofrequency carrier provides, at best, a total equivalent of about 500 to600 kbps maximum data rate transmission within acceptable bit error ratelimitations.

In contrast to this, the present invention subdivides the availableapproximately 500 to 600 kbps data rate into a relatively large numberof subchannels. In the illustrated example, the bandwidth is dividedinto sixty-four (64) subchannels 300, each providing an 8 kbps datarate. A given subchannel 300 is physically implemented by encoding atransmission with one of a number of different assignable pseudorandomcodes. For example, the 64 subchannels 300 may be defined within asingle CDMA RF carrier by using a different orthogonal code for eachdefined subchannel 300 for example, for the forward link.

As mentioned above, subchannels 300 are allocated only as needed. Forexample, multiple subchannels 300 are granted during times when aparticular ISDN subscriber unit 101 is requesting that large amounts ofdata be transferred. These subchannels 300 are quickly released duringtimes when the subscriber unit 101 is relatively lightly loaded.

The present invention relates in particular to maintaining the reverselink so that synchronization of the subchannels does not need to bereestablished each time that channels are taken away and then grantedback.

FIG. 3 is a diagram illustrating the arrangement of how the subchannelsare assigned on the reverse link. It is desirable to use a single radiocarrier signal on the reverse link to the extent possible to conservepower as well as to conserve the receiver resources which must be madeavailable at the base station. Therefore, a single 1.2288 MHz band 350is selected out of the available radio spectrum.

A relatively large number, N, such as 1000 individual subscriber unitsare then supported by using a single long pseudonoise (PN) code in aparticular way. First, a number, p, of code phases are selected from theavailable 2⁴²−1 different long code phases. A given long code phase isunique to a particular subscriber unit and never changes. As will beexplained, this is also true for supplemental code phases as well. Thecode p phases shifts are then used to provide p subchannels. Next, eachof the p subchannels are further divided into s time slots. The timeslotting is used only during the idle mode, and provides two advantages;it reduces the numbers of “maintenance” receivers in the base station,and it reduces the impact to reverse channel capacity by reducingtransmit power and thus interference. Therefore, the maximum supportablenumber of supportable subscriber units, N, is p times s. During Idlemode, use of the same PN code with different phases and time slotsprovides many different subchannels with permits using a single rakereceiver in the base station 104.

In the above mentioned channel allocation scheme, radio resources areexpected to be allocated on an as-needed basis. However, considerationmust also be given to the fact that normally, in order to set up a newCDMA channel, a given reverse link channel must be given time to acquirecode phase lock at the receiver. The present invention avoids the needto wait for each channel to acquire code phase lock each time that it isset up by several mechanisms which are described more fully below. Ingeneral, the technique is to send a maintenance signal at a rate whichis sufficient to maintain code phase lock for each subchannel even inthe absence of data.

The objective here is to minimize the size of each time slot, which inturn maximizes the number of subscribers that can be maintained in anidle mode. The size, t, of each time slot is determined by the minimumtime that it takes to guarantee phase lock between the transmitter atthe subscriber unit and the receiver in the base station. In particular,a code correlator in the receiver must receive a maintenance or“heartbeat” signal consisting of at least a certain number ofmaintenance bits over a certain unit of time. In the limit, thisheartbeat signal is sent by sending at least one bit from eachsubscriber unit on each reverse link at a predetermined time, e.g., itsdesignated time slot on a predetermined one of the N subchannels.

The minimum time slot duration, t, therefore depends upon a number offactors including the signal to noise ratio and the expected maximumvelocity of the subscriber unit within the cell. With respect to signalto noise ratio, this depends onEb/No+Iowhere Eb is the energy per bit, No is the ambient noise floor, and Io isthe mutual interference from other coded transmissions of the othersub-channels on the reverse link sharing the same spectrum. Typically,to close the link requires integration over 8 chip times at thereceiver, and a multiple of 20 times that is typically needed toguarantee detection. Therefore, about 160 chip times are typicallyrequired to correctly receive the coded signal on the reverse link. Fora 1.2288 MHz code, Tc, the chip time, is 813.33 ns, so that this minimumintegration time is about 130 μs. This in turn sets the absolute minimumduration of a data bit, and therefore, the minimum duration of a slottime, t. The minimum slot time of 130 μs means that at a maximum, 7692time slots can be made available per second for each phase coded signal.

To be consistent with certain power control group timing requirements,the time slot duration can be relaxed somewhat. For example, in theIS-95 standard, a power control group timing requirement requires apower output sample from each subscriber unit every 1.25 ms.

Once code phase lock is acquired, the duration of the heartbeat signalis determined by considering the capture or locking range of the codephase locking circuits in the receiver at the base station. For example,the receiver typically has a PN code correlator running at the code chiprate. One example of such a code correlator uses a delay lock loopconsisting of an early-late detector. A loop filter controls thebandwidth of this loop which in turn determines how long the codecorrelator must be allowed to operate before it can guarantee phaselock. This loop time constant determines the amount of “jitter” that canbe tolerated in the code correlator, such as about ⅛ of a chip time, Tc.

In the preferred embodiment, the system 100 is intended to supportso-called nomadic mobility. That is, high mobility operation withinmoving vehicles typical of cellular telephony is not expected to benecessary. Rather, the typical user of a portable computer who is activeis moving at only brisk walking speeds of about 4.5 miles per hourCMPH). At 4.5 MPH, corresponding to a velocity of 6.6 feet per second, auser will move 101 feet in ⅛ of the 1/1.2288 MHz chip time (Tc).Therefore, it will take about 101 feet divided by 6.6 feet, or about 15seconds for such a user to move a distance which is sufficiently far forhim to a point where the code phase synchronization loop cannot beguaranteed to remain locked. Therefore, as long as a completesynchronization signal is sent for a given reverse link channel every 15seconds, the reverse link loop will therefore remain in lock.

FIG. 4 is a state diagram for a reverse link bandwidth managementfunction in the subscriber unit. In an idle mode 400, a first state 401is entered in which the subscriber unit receives a time slot assignmentfor its code phase reverse channel. This time slot is only used in theidle mode. The same long code phase is pre-assigned and is permanent tothe subscriber unit.

In a next state 402, the heartbeat signal is sent in the assigned timeslots. A state 403 is then entered in which the subscriber unit monitorsits internal data buffers to determine whether additional code phasechannels are required to support the establishment of a reverse linkwith sufficient bandwidth to support and active traffic channel. If thisis not the case, then the subscriber returns to state 402 and remains inthe idle mode 400.

Prior to entering the Active state 450 from Idle mode 400, thesubscriber unit must make a request to the base station. If granted,(step 403-b), processing proceeds to step 451, and if not granted,processing proceeds to step 402. However, the subscriber unit knows thatit is assigned code phase channels in a predetermined relationship tothe code phase channel of its fundamental channel, i.e.,

 P_(n+1) ={P _(o)}

where P_(n+1) is the code phase for the new channel (n+1), and P_(o) isthe code phase assigned to the fundamental channel for the particularsubscriber. Such a code phase relationship

may be, for example, to select uniformly from the available 2⁴² codes,every 2⁴²/2¹⁰'th or every 2³²'th code phase in a system which issupporting 1024 (2¹⁰) reverse links, for a single subscriber.

A number, C, of these new code phases are therefore instantaneouslycalculated based simply upon the number of additional code phasechannels, and without the need to require code phase synchronization foreach new channel.

After step 452 is processed, a request is made for code phase channels.If granted (step 452-b), processing proceeds to step 453, and if notgranted, processing proceeds to step 451 in order to process theadditional channel requests. In a next state 453, the subscriber unitbegins transmitting its data on its assigned code phase channels. Instate 454, it continues to monitor its internal data buffers and itsassociated forward access channel to determine when to return to theidle mode 400, to state 451, to determine if new code phase channelsmust be assigned, or to state 455, where they are deallocated.

FIG. 5 is a state diagram of idle mode processing in the reverse linkmanagement function in the base station 104. In a first state 501, foreach idle subscriber unit 101, a state 502 is entered in which a storedstate of the correlators for the present time slot (p,s) from a previoussynchronization session is read. In a next state 503, an early-latecorrelator is retrained for the time slot duration, t. In a next state504, the correlator state is stored; in state 505, the loop is continuedfor each subscriber.

Equivalents

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention as defined by the appended claims.

For example, instead of ISDN, other wireline and network protocols maybe encapsulated, such as xDSL, Ethernet, and X.25, and therefore mayadvantageously use the dynamic wireless subchannel assignment schemedescribed herein.

Those skilled in the art will recognize or be able to ascertain using nomore than routine experimentation, many equivalents to the specificembodiments of the invention described specifically herein. Suchequivalents are intended to be encompassed in the scope of the claims.

1. A method for monitoring on a reverse link idling mode connectionsbetween a base station and a plurality of idling subscriber units thatare powered on, but not actively sending data, the method comprising:making available a plurality of orthogonal subchannels within at leastone Code Division Multiple Access (CDMA) radio frequency (RF) channel;assigning a shared orthogonal subchannel to at least two differentidling subscriber units, but utilizing different time slots of theshared orthogonal subchannels; for each idling subscriber unit assignedthe shared orthogonal subchannel, sending a respective heartbeat signalwithin its assigned time slot at a data rate that is low enough tomaintain bit synchronization with the base station; and tracking therespective heartbeat signals within the assigned time slots by selectingan assigned time slot within the shared orthogonal subchannel,retrieving a previous tracking of a respective heartbeat signal for anidling subscriber unit associated with the assigned time slot,determining a current tracking of the respective heartbeat signal forthe idling subscriber unit associated with the assigned time slot,updating the tracking of the idling subscriber unit associated with theassigned time slot based upon its current and previous trackings,storing the updated tracking for the idling subscriber unit associatedwith the assigned time slot, and selecting a next assigned time slotwithin the shared orthogonal subchannel, and repeating the retrieving,determining, updating and storing for a different idling subscriber unitassociated with the next selected assigned time slot.
 2. A methodaccording to claim 1 wherein for a first time tracking of the respectiveheartbeat signals within the assigned time slots, the previous trackingis a default tracking.
 3. A method according to claim 1 wherein the basestation assigns the shared orthogonal subchannel.
 4. A method accordingto claim 1 wherein the different time slots of the shared orthogonalsubchannel are uniquely assigned.
 5. A method according to claim 4wherein each idling subscriber unit sends the heartbeat signal in itsuniquely assigned time slot.
 6. A method according to claim 4 wherein anidling subscriber unit enters an active mode by sending a command signalto the base station using its uniquely assigned time slot to requestallocation of additional available orthogonal subchannels.
 7. A methodaccording to claim 1 wherein the base station sends feedback to eachidling subscriber unit relating to an adjustment of its transmit timing.8. A method according to claim 1 wherein the base station sends feedbackto each idling subscriber unit relating to an adjustment of its transmitpower.
 9. A method according to claim 1 wherein the base stationcomprises a code correlator for tracking the respective heartbeatsignals within the assigned time slots of the shared orthogonalsubchannel.
 10. A method according to claim 1 wherein the base stationcomprises an early-late correlator for tracking the respective heartbeatsignals within the assigned time slots of the shared orthogonalsubchannel.
 11. A method for monitoring idling mode connections betweena base station and a plurality of idling subscriber units that arepowered on, but not actively sending data, the method comprising: makingavailable a plurality of orthogonal subchannels within at least one CodeDivision Multiple Access (CDMA) radio frequency (RF) channel; assigninga shared orthogonal subchannel to at least two different idlingsubscriber units, but utilizing different time slots of the sharedorthogonal subchannels; for each idling subscriber unit assigned theshared orthogonal subchannel, sending a respective heartbeat signalwithin its assigned time slot at a data rate that is low enough tomaintain bit synchronization with the base station; and tracking therespective heartbeat signals within the assigned time slots by selectingan assigned time slot within the shared orthogonal subchannel,retrieving a previous tracking of a respective heartbeat signal for anidling subscriber unit associated with the assigned time slot,determining a current tracking of the respective heartbeat signal forthe idling subscriber unit associated with the assigned time slot, andupdating the tracking of the idling subscriber unit associated with theassigned time slot based upon its current and previous trackings.
 12. Amethod according to claim 11 wherein tracking the respective heartbeatsignals further comprises storing the updated tracking for the idlingsubscriber unit associated with the assigned time slot.
 13. A methodaccording to claim 12 wherein tracking the respective heartbeat signalsfurther comprises selecting a next assigned time slot within the sharedorthogonal subchannel, and repeating the retrieving, determining,updating and storing for a different idling subscriber unit associatedwith the next selected assigned time slot.
 14. A method according toclaim 11 wherein for a first time tracking of the respective heartbeatsignals within the assigned time slots, the previous tracking is adefault tracking.
 15. A method according to claim 11 wherein the basestation assigns the shared orthogonal subchannel.
 16. A method accordingto claim 11 wherein the different time slots of the shared orthogonalsubchannel are uniquely assigned.
 17. A method according to claim 16wherein each idling subscriber unit sends the heartbeat signal in itsuniquely assigned time slot.
 18. A method according to claim 16 whereinan idling subscriber unit enters an active mode by sending a commandsignal to the base station using its uniquely assigned time slot torequest allocation of additional available orthogonal subchannels.
 19. Amethod according to claim 11 wherein the base station sends feedback toeach idling subscriber unit relating to an adjustment of its transmittiming.
 20. A method according to claim 11 wherein the base stationsends feedback to each idling subscriber unit relating to an adjustmentof its transmit power.
 21. A method according to claim 11 wherein thebase station comprises a code-correlator for tracking the respectiveheartbeat signals within the assigned time slots of the sharedorthogonal subchannel.
 22. A method according to claim 11 wherein thebase station comprises an early-late correlator for tracking therespective heartbeat signals within the assigned time slots of theshared orthogonal subchannel.
 23. A base station comprising: a pluralityof Code Division Multiple Access (CDMA) transceivers; and a bandwidthmanagement circuit connected to said plurality of CDMA transceivers formonitoring idling mode connections with a plurality of idling subscriberunits that are powered on, but not actively sending data, said bandwidthmanagement circuit making available a plurality of orthogonalsubchannels within at least one CDMA radio frequency (RF) channel,assigning a shared orthogonal subchannel to at least two differentidling subscriber units, but utilizing different time slots of theshared orthogonal subchannel, receiving from each idling subscriber unitassigned the shared orthogonal subchannel, a respective heartbeat signalwithin its assigned time slot at a data rate that is low enough tomaintain bit synchronization with the base station, and tracking therespective heartbeat signals within the assigned time slots by selectingan assigned time slot within the shared orthogonal subchannel,retrieving a previous tracking of a respective heartbeat signal for anidling subscriber unit associated with the assigned time slot,determining a current tracking of the respective heartbeat signal forthe idling subscriber unit associated with the assigned time slot, andupdating the tracking of the idling subscriber unit associated with theassigned time slot based upon its current and previous trackings.
 24. Abase station according to claim 23 wherein tracking the respectiveheartbeat signals by said bandwidth management circuit further comprisesstoring the updated tracking for the idling subscriber unit associatedwith the assigned time slot.
 25. A base station according to claim 24wherein tracking the respective heartbeat signals by said bandwidthmanagement circuit further comprises selecting a next assigned time slotwithin the shared orthogonal subchannel, and repeating the retrieving,determining, updating and storing for a different idling subscriber unitassociated with the next selected assigned time slot.
 26. A base stationaccording to claim 23 wherein for a first time tracking of therespective heartbeat signals within the assigned time slots by saidbandwidth management circuit, the previous tracking is a defaulttracking.
 27. A base station according to claim 23 wherein the differenttime slots of the shared orthogonal subchannel are uniquely assigned.28. A base station according to claim 27 wherein each idling subscriberunit sends the heartbeat signal in its uniquely assigned time slot. 29.A base station according to claim 23 wherein one of said plurality ofCDMA transceivers sends feedback to each idling subscriber unit relatingto an adjustment of its transmit timing.
 30. A base station according toclaim 23 wherein one of said plurality of CDMA transceivers sendsfeedback to each idling subscriber unit relating to an adjustment of itstransmit power.
 31. A base station according to claim 23 wherein saidbandwidth management circuit comprises a code-correlator for trackingthe respective heartbeat signals within the assigned time slots of theshared orthogonal subchannel.
 32. A base station according to claim 23wherein said bandwidth management circuit comprises an early-latecorrelator for tracking the respective heartbeat signals within theassigned time slots of the shared orthogonal subchannel.